Pump assembly comprising a plurality of jet pumps

ABSTRACT

A pump assembly includes a housing ( 50 ) and a plurality of jet pumps ( 52 ) arranged within the housing. The housing ( 50 ) includes a HP inlet ( 54 ), a LP inlet ( 58 ) and an outlet ( 56 ) and is divided internally into a HP zone ( 62 ), a LP zone ( 64 ) and an outlet zone ( 66 ). Each jet pump ( 52 ) includes a nozzle assembly ( 80 ), a mixing tube ( 82 ) and a diffuser ( 84 ), and has a HP inlet ( 74 ) located in the HP zone, a LP inlet ( 78 ) located in the LP zone, and an outlet ( 76 ) located in the outlet zone.

The present invention relates to a pump assembly and in particular, but not exclusively, to a pump assembly using jet pumps for use in the oil and gas industries.

Jet pumps or eductors are passive devices that use energy from a high pressure (HP) fluid source to boost the pressure of a low pressure (LP) fluid. The terms jet pump, eductor, ejector and gas jet compressor are used in various industries and refer to the same general type of device.

FIG. 1 shows the key features of a typical jet pump. HP fluid from a HP source 2 passes through a conduit 4 to a jet pump 6, where it passes through constriction known as a nozzle 8 that increases its velocity. In this way part of the potential (pressure) energy of the HP fluid is converted to kinetic energy (high velocity fluid). As a result, the pressure of the fluid in front of the nozzle 8 drops significantly. LP fluids from a LP source 10 pass through a conduit 12 and are introduced at this point and entrained in the flow. The mixture of fluids then passes through a mixing tube 14 where momentum and energy are exchanged between the HP and LP fluids. The mixture finally passes through an expanding diffuser 16 where the velocity of flow normalises and pressure recovery takes place. The pressure at the outlet 18 of the jet pump will be at an intermediate value between the pressures of the HP and LP sources 2, 10.

Jet pumps have been used successfully in a variety of applications onshore or near the bottom of oil or gas wells. The HP flow is gas or a high pressure liquid such as oil or water. The LP flow could be gas, or liquid (oil and water), or a mixture of the two.

In applications such as those for the oil and gas industry, the operating conditions often change with time. These changes may demand changes to the jet pump design or the internal dimensions of the jet pump in order to optimise the design and get the best performance under the new conditions. These changes demand using a new jet pump with new dimensions for its internal key components such as the nozzle and the mixing tube. Supplying and installing the new jet pump is costly and may require that production is interrupted for a substantial period.

Jet pumps with interchangeable internals (the nozzle assembly, and the mixing tube/diffuser assembly) have been designed and supplied. An example is shown in FIG. 2. This jet pump 6 includes a housing 20 with a HP inlet 22, a LP inlet 24 and an outlet 26. Mounted within the housing 20 are a nozzle assembly 28 and a separate mixer/diffuser tube 30. These features enable the main body or housing 20 of the unit to be kept and internals with new dimensions to be inserted and fixed inside the main body as required, according to the operating conditions.

In some applications, only a change in the nozzle of the jet pump may be necessary. For such applications a multi-nozzle pump assembly has been proposed, as shown in FIG. 3. In this arrangement, a single housing 32 is provided, which accommodates a plurality of nozzles 34. The housing has a LP inlet 36 and a single mixing tube/diffuser 38 for receiving the mixture of HP and LP fluids. Each nozzle 34 has a valve 40 to switch it on or off, so as to supply the desired total amount of HP fluid through feed lines 42. This increases the size of the pump assembly because of the need for a valve for each nozzle, and this is not usually welcomed by the industry. Furthermore, the efficiency of the pump assembly is limited by the provision of a single mixing tube/diffuser, which prevents it from operating efficiently over a wide range of flow rates.

With increases in the applications of jet pumps and the development of new subsea production systems there is a need for a jet pump assembly suitable for subsea applications. Subsea production systems may consist of a variety of components such as manifolds, valves and in some cases booster pumps and separators, all of which are located on the sea bed to avoid the need for costly offshore platforms. All equipment that is installed subsea for any function needs to be highly reliable, with little to no maintenance requirement or changes to design requiring retrieval of the unit to surface, as the cost of retrieving such units for maintenance, repair, or modification is very high, especially in deep water applications.

It is also desirable in many offshore platforms to minimise maintenance work, and to minimise the need to isolate and de-pressurise the jet pump and replace its internal components.

It is an object of the present invention to provide a pump apparatus that mitigates one or more of the aforesaid disadvantages.

According to one aspect of the present invention there is provided a pump assembly comprising a housing and a plurality of jet pumps arranged within the housing, wherein the housing includes a HP inlet, a LP inlet and an outlet and is divided internally by partitions into a HP zone, a LP zone and an outlet zone, said partitions comprising a first partition between the HP zone and the LP zone, and a second partition between the LP zone and the outlet zone, said LP zone being located longitudinally between the HP zone and the outlet zone, and each jet pump includes a nozzle assembly, a mixing tube and a diffuser and comprises an elongate tubular body having an HP inlet at a first end of the body, an outlet at a second end of the tubular body and a LP inlet between the first and second ends, wherein each jet pump is mounted within the housing with the HP inlet located in the HP zone, the LP inlet located in the LP zone, and the outlet located in the outlet zone, and each jet pump extends through and is sealed to the first and second partitions.

By providing a plurality of jet pumps within a single housing, it is possible to adapt the pump apparatus to different flow rates and different flow regimes (for example, different proportions of gas and liquid). This ensures high efficiency over a wide range of flow regimes and capacities. Further, because each jet pump includes a nozzle assembly, a mixing tube and a diffuser, it is capable of efficient operation, as the nozzle assembly may be matched specifically to the mixing tube and the diffuser design.

The pump assembly can also be modularised, consisting of a number of standard, off-the-shelf, components that can be selected according to specific production conditions including, for example, the flow rate, pressure and flow regime of the produced fluids. These components can then be assembled relatively quickly and easily, allowing a custom-designed pump assembly to be supplied quickly and at relatively low cost.

Preferably, each jet pump is sealed to the partitions, for example by means of O-ring seals or by welding.

Preferably, the housing is T-shaped, having a longitudinal axis and a transverse axis, the HP inlet being located at one end of the longitudinal axis, the outlet being located at the opposite end of the longitudinal axis and the LP inlet being located on the transverse axis. Advantageously, the housing comprises a T-section pipe.

Preferably, at least some of the jet pumps have common external dimensions. More preferably, all the jet pumps have common external dimensions, or they all have “standard” external dimensions, selected for example from two or more alternative sets of dimensions.

Preferably, at least one of the jet pumps is substantially cylindrical having a HP inlet at one end, an outlet at an opposite end and a LP inlet in a side thereof.

Advantageously, the pump assembly includes isolation means for isolating at least one of the jet pumps. This allows individual jet pumps to be turned on or off, thereby adapting the system to changes in operating conditions.

The isolation means preferably comprises means for stopping the HP inlet, the LP inlet and/or the outlet of at least one of the jet pumps. Preferably, the isolation means comprises means for stopping two of the three inlet and outlet vents.

The pump assembly preferably includes an actuator for actuating the isolation means to isolate individual jet pumps, allowing the system to be adapted to changes in operating conditions from a remote location. This is particularly helpful in apparatus intend for use in subsea operations. Preferably, the actuator comprises a hydraulically-driven valve.

In a preferred embodiment, the invention provides a modularised, multi jet pump unit, which allows the operator to use any number of standard jet pump units as needed, depending on the field conditions, without having to isolate the system, remove the old internals and introduce new sets of internals. Each jet pump unit consists of the same key components of a nozzle, a mixing tube and a diffuser. The multiple jet pump units are housed in a containment pressure vessel or pipe section for ease of handling and for isolating the system against exposure to subsea environment, or in the case of offshore platforms achieve the full pressure rating of the total jet pump system. The key features of the new system are described below.

Certain embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a first known jet pump system;

FIG. 2 is a sectional isometric view of a second known jet pump system;

FIG. 3 is a sectional side view of a third known multi-nozzle jet pump system;

FIG. 4 is a sectional side view of a pump assembly according to an embodiment of the invention;

FIG. 5 is a cross-sectional view on live IV-IV of FIG. 4;

FIG. 6 is a sectional side view of a jet pump comprising part of the pump assembly of FIG. 4, and

FIG. 7 is a partial sectional view of another jet pump having hydraulically-activated valve.

The pump assembly shown in FIGS. 4, 5 and 6 comprises a housing 50 and a plurality of jet pumps 52 arranged within the housing 50.

In this example, the housing 50 comprises a T-section pipe is T-shaped having a longitudinal axis and a transverse axis. An HP inlet 54 is located at one end of the longitudinal axis, an outlet 56 is located at the opposite end of the longitudinal axis and a LP inlet 58 is located on the transverse axis. The HP and LP inlets 54, 58 and the outlet 56 are each provided with flanges 60 for connection to external pipelines (not shown).

The housing 50 is divided internally into a HP zone 62, a LP zone 64 and an outlet zone 66 by two partition walls 68, 70 the LP zone being located longitudinally between the HP zone and the outlet zone. The first partition wall 68 is located between the HP zone 62 and the LP zone 64, and the second partition wall 70 is located between the LP zone and the outlet zone. Each of these partition walls 68, 70 includes a plurality of apertures 72 for receiving the individual jet pumps 52. In the embodiment shown in FIGS. 4 to 6 nine apertures 72 are provided in each wall 68, 70, eight of these being arranged in a circle around the ninth aperture. These numbers may vary depending on field conditions and expectations of the extent of changes during the service life of the system.

Each jet pump 52 is substantially cylindrical comprising an elongate tubular body 73 having a HP inlet 74 at a first end of the body, an outlet 76 at a second end of the body and a LP inlet vent 78 in a side of the body between the first and second ends thereof. It is supported by the partition walls 68, 70 so that the HP inlet 74 is located in the HP zone 62, the LP inlet 78 is located in the LP zone 64 and the outlet 76 is located in the outlet zone 66. Internally, each jet pump 52 includes a nozzle assembly 80, a mixing tube 82 and a diffuser 84.

O-ring seals 86 are provided on the external cylindrical surface of the jet pump 52 to form a hermetic seal with the two partition walls 68, 70. Alternatively, the jet pumps 52 may be welded permanently to the partition walls 68, 70.

As shown in FIG. 6, each jet pump 52 may be provided with plugs 88 that can be screwed into the HP inlet 74 and the outlet 76 to prevent any flow of fluid, thereby isolating the jet pump 52. Sealing rings 90 are provided to ensure a tight seal between the plug 88 and the end of the jet pump 52. By inserting or removing these plugs 88, the number of operational jet pumps 52 in the pump apparatus can be changed, thus allowing the pump apparatus to be adapted to different flow conditions, without changing the structure of the pump apparatus. To isolate the jet pump, plugs 88 can be fitted to any two of the three inlets and outlet vents 74, 76, 78, or to all three vents.

If the jet pumps 52 are identical, the capacity of the pump apparatus can be adjusted by increasing or decreasing the number of isolated jet pumps. Alternatively, jet pumps 52 with different flow capacities can be fitted to provide a wider range of flow capacity, or different types of jet pump can be used so that the pump apparatus can be adapted to different flow regimes (for example, different amounts of gas and liquid).

Preferably, the jet pumps 52 all have identical external dimensions (even if they have different flow capacities or are of different types), so that they can be supplied as standard “off the shelf” products, which can then be selected and fitted into a standard housing, according to the requirements of the application for which they are intended, including for example the flow rate, pressure and flow regime of the produced fluids.

If the plugs 88 are fitted manually, for example by screwing them into the ends of the jet pump 52, it will be necessary first to depressurise and isolate the pump apparatus, so as to provide access to the jet pumps. Although this is a somewhat time-consuming process, it is nevertheless considerably quicker and less expensive than adapting or removing and replacing a conventional jet pump.

For subsea installations, it may be impractical to change the configuration of the pump apparatus manually. A pump apparatus intended for use in this situation may therefore be provided with actuator-operated plugs for isolating individual jet pumps. These plugs may for example be hydraulically actuated. FIG. 7 shows such a plugging arrangement using a hydraulically-driven valve.

In this example a piston 95 is provided at the HP inlet end of the jet pump unit 52. The regions of the jet pump body on either side of the piston 95 are isolated by ring seals 98. These seals 98 isolate fully the small gap between the outer surface of the piston 95 and the inner surface of the jet pump 52. The piston 95 can slide along the inner body of the jet pump to expose or to isolate a port 96, which comprises the HP inlet through which HP fluid enters the jet pump. There is a seal ring 97 around the port 96, which acts with the piston 95 to seal the HP inlet and prevent the passage of fluids beyond the port 96.

Under operating mode a spring 94 pushes the piston 95 to a position which exposes the port 96 and opens the flow passage into the jet pump. When the piston 95 is to be moved to cover and seal the port 96, hydraulic fluid is injected via a line 92 into a pressure chamber 93 between the piston 95 and a removable screwed end cap 91. This pressure pushes the piston 95 against the spring 94 and closes the port 96.

Such a piston assembly or similar can be applied to both the discharge end and the HP inlet end of the jet pump.

In summary, according to an embodiment of the invention, the multi jet pump assembly consists of several small standardised jet pumps assembled to operate in parallel. The number can be any, varying from two to several, depending on the application. The system is designed so that at any time any number of jet pump units can be operational to match the operating conditions of that time. All units can be of identical external design to minimise cost, or if needed they can consist of two or more groups of similar size. In this case each jet pump is always of optimum design as it always handles the flow for which it was designed, even if the total HP or LP flow changes significantly.

This feature has a number of benefits which justify its use for subsea or offshore applications:

-   -   Being made of several small jet pumps the overall length of the         unit is significantly less than that of a single jet pump         performing the same duty as the combined jet pumps. Normally,         the total length of each jet pump is equal to a multiplier of         its mixing tube and diffuser diameter. Therefore for small         mixing tube diameters of the modularised jet pumps the total         length is reduced significantly. Typical multiplier for the         length of a jet pump is 20 to 40 times the diameter of the         mixing tube, depending on applications.     -   As the operating conditions change, there is no need to modify         or change the internals of the jet pump as in this case the         change is achieved by only changing the number of jet pump units         in operation within the bundle.     -   By eliminating the need for changing the internals of the jet         pump, there is no need to interrupt production to remove the jet         pumps and replace them with new units or sets of internals.     -   Switching individual jet pumps on or off will take little time,         compared with changing the internals of a jet pump or the costly         process of changing a whole jet pump.     -   The arrangement can also be used for onshore or offshore         applications with benefits such as using standard single sized         units which can be manufactured in advance and used whenever         needed, without having to wait for the manufacture of new         internals.

The system therefore consists in a preferred embodiment of the following key features as shown in FIGS. 4, 5 and 6:

-   -   A containment vessel 50, which houses the group of jet pump         units 52;     -   Single vents for the inlet 54 for the HP flow, inlet 58 for the         LP flow and the outlet 56 of the system;     -   The containment vessel 50 consists of a Tee section to provide         the inlet point 58 for the LP flow. The two other end flanged         sections are allocated to HP flow inlet 54 and the common outlet         point 56;     -   The vessel is divided into three separate pressure zones 62, 64,         66 comprising the HP, LP and the discharge sections;     -   Each pressure zone 62, 64, 66 acts as a manifold to feed the HP         and LP inlets 74, 78 and the discharge points 76 of the jet         pumps;     -   The three pressure sections are separated from one another by         isolation plates 68, 70, which are welded to the main         containment vessel.     -   The individual jet pump units 52 pass through each isolation         plate 68, 70 and are welded to the isolating plates 68, 70 or         are equipped with sealing rings 86 or equivalent as they pass         through each isolation plate, to ensure the operating pressure         of the HP, LP and discharge manifold is maintained and each part         is isolated from the neighbouring part;     -   To enable the isolation of individual jet pumps, the system is         equipped with a set of two isolation valves or plugs 88 at each         end of each jet pump. This enables the individual jet pumps to         be switched on or off, if and when desired. This feature is         shown in FIG. 6, showing the plug arrangement. The plug 88 is         screwed into the HP inlet 74 and the discharge end 76.         Alternatively, instead of the plug, a piston valve similar to         that shown in FIG. 7 can be hydraulically pushed in or out of         each end of the jet pump to achieve the isolation or functioning         of each jet pump without interrupting production. Only two out         of the three inlet and outlet vents needs to be plugged to         isolate the jet pump. If isolation plugs are used, each plug is         equipped with sealing rings to plug and isolate the relevant         section effectively. 

1. A pump assembly comprising a housing and a plurality of jet pumps arranged within the housing, wherein the housing includes a HP inlet, a LP inlet and an outlet and is divided internally by partitions into a HP zone, a LP zone and an outlet zone, said partitions comprising a first partition between the HP zone and the LP zone, and a second partition between the LP zone and the outlet zone, said LP zone being located longitudinally between the HP zone and the outlet zone, and each jet pump includes a nozzle assembly, a mixing tube and a diffuser and comprises an elongate tubular body having an HP inlet at a first end of the body, an outlet at a second end of the tubular body and a LP inlet between the first and second ends, wherein each jet pump is mounted within the housing with the HP inlet located in the HP zone, the LP inlet located in the LP zone, and the outlet located in the outlet zone, and each jet pump extends through and is sealed to the first and second partitions.
 2. A pump assembly according to claim 1, wherein the housing is T-shaped comprising a longitudinal axis and a transverse axis, the HP inlet being located at one end of the longitudinal axis, the outlet being located at the opposite end of the longitudinal axis and the LP inlet being located on the transverse axis.
 3. A pump assembly according to claim 2, wherein the housing comprises a T-section pipe.
 4. A pump assembly according to claim 3, wherein at least some of the jet pumps have common external dimensions.
 5. A pump assembly according to claim 4, wherein at least one of the jet pumps is substantially cylindrical having a HP inlet at one end, an outlet at an opposite end and a LP inlet in a side thereof.
 6. A pump assembly according to claim 5, further including isolation means for isolating at least one of the jet pumps.
 7. A pump assembly according to claim 6, wherein the isolation means comprises means for stopping the HP inlet, the LP inlet and/or the outlet of at least one of the jet pumps.
 8. A pump assembly according to claim 7, further including an actuator for actuating the isolation means.
 9. A pump assembly according to claim 8, wherein the actuator comprises a hydraulically-driven valve.
 10. A pump assembly according to claim 2, wherein at least some of the jet pumps have common external dimensions.
 11. A pump assembly according to claim 1, wherein at least some of the jet pumps have common external dimensions.
 12. A pump assembly according to claim 3, wherein at least one of the jet pumps is substantially cylindrical having a HP inlet at one end, an outlet at an opposite end and a LP inlet in a side thereof.
 13. A pump assembly according to claim 2, wherein at least one of the jet pumps is substantially cylindrical having a HP inlet at one end, an outlet at an opposite end and a LP inlet in a side thereof.
 14. A pump assembly according to claim 1, wherein at least one of the jet pumps is substantially cylindrical having a HP inlet at one end, an outlet at an opposite end and a LP inlet in a side thereof.
 15. A pump assembly according to claim 4, further including isolation means for isolating at least one of the jet pumps.
 16. A pump assembly according to claim 3, further including isolation means for isolating at least one of the jet pumps.
 17. A pump assembly according to claim 2, further including isolation means for isolating at least one of the jet pumps.
 18. A pump assembly according to claim 1, further including isolation means for isolating at least one of the jet pumps.
 19. A pump assembly according to claim 6, further including an actuator for actuating the isolation means. 